A thermal printer has been used as a printer of a facsimile, a register, and so forth. The thermal printer comprises a thermal head and a platen roller. As an example of thermal heads mountable in the thermal printer, there is known a thermal head having a plurality of heat-generating elements and a protective layer. The plurality of heat-generating elements are arranged on a substrate. The protective layer is disposed on the plurality of heat-generating elements and thus acts to protect the heat-generating elements. The platen roller acts to press a recording medium against the protective layer disposed on the heat-generating elements. Examples of the recording medium include thermal paper. In such a thermal printer, the heat-generating elements are operated to produce heat in accordance with a desired image, and also a recording medium is pressed against the protective layer disposed on the heat-generating elements in a heating state by the platen roller. In this way, heat produced by the heat-generating element is transferred to the recording medium. Desired printing onto the recording medium is accomplished by repeating such process steps.
In such a thermal printer, however, the protective layer of the thermal head mounted therein could undergo abrasion due to contact with the recording medium, which results in a decline in the function of the protective layer. In view of this a thermal head has been developed that employs a highly abrasion-resistant diamond-like carbon film (hereafter referred to as “DLC film”) as a material for forming the protective layer. A thermal head of this type is disclosed for example in Patent Literature 1.
However, in the thermal head disclosed in Patent Literature 1, the DLC film could be combined with oxygen in the air and consequently sublime. Such a sublimation could occur for example in a so-called no-paper printing condition, which is a state where a heating resistive element is driven while recording-medium conveyance is suspended due to a conveyance abnormality in a conveying section of the thermal printer for conveying recording media. In the event of sublimation of the DLC film under such a condition, the abrasion resistance of the thermal head could be deteriorated significantly, which makes it impossible to properly maintain the function of the protective layer.    Patent Literature 1: Japanese Unexamined Patent Publication JP-A 7-132628 (1995)